1. Field of the Invention
The present invention relates to apparatus for supplying developer for use in electrophotography as well as a developing apparatus provided with the developer supply apparatus.
2. Description of the Prior Art
For electrophotographic developing apparatus there are used, as electrophotographic developing agent, dry colored particles which are generally called toner. Regarding such dry toner, it is well known that a difficulty arises in supplying the toner from a toner reservoir to a container for development due to its poor fluidity.
For this reason, the procedure of supplying toner hitherto conventionally employed was very troublesome. The operator visually observes the copy sheet having thereon a toner image after developing and when the density of the toner image is low and the operator judges the copy to be too thin, he opens the package of a container containing a large volume of toner. Then the operator pours a suitable amount of toner into the toner container for development.
Also, such toner supplying means is known that is adapted for automatically effecting a supply of toner. In this case, the supply of toner is carried out portionwise in an optimum amount according as the number of copies then made.
However, toner particles are very fine particles and therefore toner is poor in fluidity so that it is apt to bridging within the toner reservoir. Therefore, it is a difficult task to supply such toner to a developing container with sufficient accuracy. In particular, when toner becomes sticky because of heat and/or humidity, the fluidity of toner is reduced to a great extent.
To avoid the problems involved in use of toner, for the conventional apparatus there is provided in the toner reservoir a separate stirring device (cf. U.S. Pat. No. 3,196,831 specification, in particular FIG. 7 thereof) or other similar additional means, for example, spiral toner conveying means. However, such additional means, whether it may be toner stirring means or spiral toner conveying means, gives rise to another problem. Namely, such means forms a cavity of toner within the toner reservoir and makes the remainder of toner around the cavity stick onto the inner wall surface of the reservoir which is well known as the so-called bridging phenomenon. When such bridging once occurs, it often blocks further transportation or flow of toner.
With any of the above described means of the prior art, it is impossible to allocate just an optimum amount of toner to one supply, when a supply of toner becomes necessary, responding to the result of measurement, for example, of toner density and then to correctly effect supplying the allocated toner to the reservoir.
A solution to the problem of bridging is disclosed in U.S. Pat. No. 3,606,864 (refer to FIGS. 1 through 3 and the relevant description). According to the solution, the toner reservoir is formed to have a dural structure opposed to the developer applicator. More particularly, the reservoir comprises a stationary cylindrical housing and a rotatable hollow cylinder disposed within the housing. The two cylinders each have one slot extending along the length of each cylinder passing through the wall. Toner is contained in the inner rotatable cylinder and the latter thus charged with toner is driven to rotate. When the two slots coincide with each other in position, the toner contained in the inner cylinder is allowed to be discharged from the inner cylinder to the outside of the outer cylindrical housing through the slots.
This known toner supply device has various drawbacks. Firstly, sealing of the rotary part of the device is very troublesome. Secondly, when the toner contained in the cylinder is completely consumed and the supply device is emptied, exchanging of the empty container for new one or recharging the empty container with toner is not easy to carry out. Finally, it is complicated in structure.